Stepped bottom for boat



7 Sept. 22, 1964. J. PLUM 3,149,351

STEPPED BOTTOM FOR BOAT Filed Feb. 26, 1963 2 Sheets-Sheet 1 /5 SURFACE DEPRESSION snu. WATER SURFACE ACCELLERATING FLOW 1 T0 PROPELLER WATER FLOW umscrrore OF FORWARD uonon nus TO THRUST DEVELOPED BY ROTATING PROPELLER INVENTOR John Plum BY Maw ATTORNEY Sept. 22, 1964 J. PLUM 3,149,351

STEPPED BOTTOM FOR BOAT Filed Feb. 26, 1963 2 Sheets-Sheet 2 RWENTOR John Plum MEN ATTORNEY United States Patent 3,149,351 STEPPED BOTTGM FOR BOAT John Plum, Washington, D.C., assignor to Lone Star Boat Company, Plano, Tex., a corporation of Texas Filed Feb. 26, 1963, Ser. No. 261,936 3 Claims. (Ci. 9-6) This invention is concerned with boats, and is particularly concerned with a novel design for the bottom of a boat which reduces the drag in the water at high speeds, to thereby increase the speed of the boat and provide geater stability of the boat at high speeds.

In pleasure and speed boats it is generally agreed that at high speeds the width of the running bottom which contacts the water should be less and less in order to reduce the drag of the boat against the water, while at the same time maintaining the necessary lift to support the hull of the boat. On the other hand, at low speeds, the beam of the boat which contacts the Water should be greater in order to maintain the necessary lift to support the hull at low speeds.

The present invention is intended to provide a design for the lower surface of the hull of a boat wherein the surface thereof contacting the water is progressively reduced as the speed of the boat increases, thereby reducing the drag in direct relationship to the increase in speed of the boat.

This is accomplished by the provision of diagonal and transversely disposed steps in the rear portion of the bottom of the hull. It has been found by experiment that this construction does not materially affect the overall stability of the boat, but permits considerable increase in speed and stability of the boat at higher speeds, due to the fact that the rear portion of the bottom of the hull contributes very little to the general lift and stability of the hull, but contributes a great deal to the increased drag resistance of the hull at high speeds.

Therefore, by progressively reducing the drag of the bottom of the hull as the speed increases, the overall speed of the boat is increased, and at the same time greatly improves the stability and riding characteristics of the boat at higher speeds.

Another feature of the present invention is the provision of a transverse step at the rear of the bottom of the hull, providing a recessed area at the rear of the bottom of the hull which spaces the bottom of the hull from the water sufficiently that at high speeds the suction caused by the propeller at the rear of the boat does not have a tendency to suck the rear of the boat under the surface of the water to increase the drag on the hull.

Other and further objects of the invention will become apparent upon reading the detailed specification hereinafter following, and by referring to the drawings annexed hereto.

A suitable embodiment of the invention is shown in the attached drawings wherein:

FIGURE I is a side elevational view of a boat incorporating the novel hull bottom design;

FIGURE II is a bottom plan view of the boat incorporating the novel design;

FIGURE III is a diagrammatic view illustrating the surface depression formed in the water surface by propeller as it progresses through the water;

FiGURE IV is a transverse, cross-sectional view taken on the line IVIV of FIGURE 1;

FIGURE V is a transverse, cross-sectional view taken on a line VV of FIGURE 1;

FIGURE VI is a transverse, cross-sectional view taken on the line VIVI of FIGURE 1;

FIGURE VII is a transverse, cross-sectional view taken on the line VIIVII of FIGURE I; and

FIGURE VIII is a fragmentary, cross-sectional view "Ice showing the diagonal step in the bottom of the hull taken on the line VIIIVIII of FIGURE II.

Numeral references are employed to designate the various parts shown in the drawings, and like numerals indicate like parts throughout the various figures of the drawings.

The numeral 1 generally indicates the hull of the boat, and the numeral 2 indicates the bottom of the hull.

The forward chine lines which separate the upper part of the hull from the lower part thereof are indicated by the numeral 3. The forward chine lines 3 curve arcuately backwardly longitudinally of the hull and merge into the rear chine lines 4.

Diagonally disposed steps 5 are formed in the bottom of the hull which are intersected by transverse step 7 which intersects and terminates the keel 6 at a point spaced from the rear end of the boat.

The diagonally disposed steps 5, provide triangular shaped depressed areas 9 at each side of the bottom of the hull. The lateral stepped edge 7 joins with diagonally disposed stepped edges 8 to form recessed area 10 at the rear of the boat which is bounded by the transverse wall 7 and diagonally disposed walls 8. It will be observed that the bottom wall of the recess 10 is also diagonally disposed to provide a diagonal trailing edge 10a in the recessed areav The stepped walls 5 provide a progressively narrower bottom area 11, which terminates with the transverse step 7.

The numeral 12 indicates the approximate forward extent of the water contact with the bottom hull 2 of the boat, when the boat is moving at high speed. Preferably this line is spaced forwardly of the intersection of the diagonal steps 5 with longitudinal chines 3 for the purposes which will be hereinafter mentioned.

As shown diagrammatically in FIGURE 111, a propeller 13, driven by an outboard motor 14 attached to the rear of the boat, runs underneath the surface of the water as the boat is propelled forwardly therethrough. Normally the propeller has a tendency to draw water therethrough from the surface, forming a surface depression indicated at 16, forwardly of the propeller. Said surface depression has a tendency to provide a suction to suck the rear of the boat lower into the water, increasing the drag of the boat.

This phenomena is compensated for in the present construction wherein the depressed area 10 at the rear of the boat, spaces the diagonal trailing edge 10a above the surface depression 16, sufficiently that the bottom of the boat is not depressed into the water to provide a drag, thus overcoming this shortcoming.

The operation and function of the boat incorporating the novel bottom hull design described herein, is as follows:

When the boat is not in motion, the water line is indicated by the numeral 17, it being noted that the bottom hull 2 is submerged in the water including the diagonal steps 5, the depressed areas 9, the transverse step 7, diagonal steps 8, and the depressed area 19.

As the boat is accelerated forwardly, a displacement type of operation takes place, which raises the hull of the boat from the water from front to rear as the speed increases. At about 15 to 18 miles per hour, the bottom of the hull enters the planing condition at which the front end begins to lift from the water. As the speed accelerates to about 22 miles per hour, the depressed area 10 begins to separate from the water, substantially reducing the drag of the boat, allowing the boat to rapidly accelerate to about 28 miles per hour. At approximately such speed, the depressed areas 9 begin to separate from the water, and they will be completely separated from the water at approximately 38 miles per hour. This also substantially reduces the drag, allowing further rapid acceleration of the "boat to around 50 miles per hour at about 100 horsepower.

It'will be noted thatat this speed the wetted area of the bottom of the boat is that outlined by the diagonal line 5, transverse line 7 and the diagonally disposed water lines 12, and that this area converges rearwardly.

The diagonally disposed lines 12are imaginary lines which'are intended to designate the beginning of solid 'water flow underneath the hull at high speed. This line moves forward of the location shown on the drawing as speed decreases and when the speed is increased 'to approximately 55'miles per hour, then the lines 12 will move somewhat aft of the location shown on FIGURE I. However, it is desirable that the point Where the solid water lines 12 intersect the forward chines 3 should be approximately 12 to 18 inches ahead of the point where the stepped diagonal chinesS'intersect the forward chines 3. Such is desirable in order to prevent'spray from being thrown back behind the steps 5 so that the water will be sucked up into the recessed area 9. It is important that all spray be directed outwardly to clear the side of the hull before it reaches the recessed area 9.

At high speed the solid water wetted surface is bounded by the stagnation lines 12 and is bordered at the rear by the diagonal stepped chine lines 5 and the transverse stepped line 7. The configuration of the diagonal stepped chines 5 and the location of the transverse stepped wall 7 may be calculated in order to maintain the center of pressure location at high speed more or less in the same area to thereby maintain a balanced attitude of the hull, both at high and low speeds.

In tests it has been found that a propeller running underneath water causes a depression ahead of its path by reason of the acceleration of water approaching the propeller forwardly thereof. This acceleration causes a dip in the surface underneath the rear hull of the boat, which causes a suction at'the rear end of the boat, thereby tending to lower the stern in the water and raise the bow, increasing the drag. This condition becomes more and more pronounced as speed increases. The transverse step 7 and diagonal steps 8 are so arranged and spaced from the rear of the boat to provide a recessed area 10 directly over the depression formed by the propeller, as to remove the bottom of the hull from the water surface ahead of the propeller in order to avoid the suction on the rear of the hull, as hereinbefore described. This greatly increases the speed and stability of the boat at higher speed.

Another advantage of the design hereinbefore described is that upon making turns the boat is much more stable, because when the boat is turned, the recessed area 9 on the side toward the turn immediately contacts the water and contributes to the general stability of the hull as the turn is being negotiated.

The upward sloping stern surface 10a also contributes to an easier low drag condition at low speeds, because the water is able to come up to the surface from underneath the boat much quicker than it normally would. Furthermore, the provision of such recessed surface with a sloping -Wall will also prevent the boat frombeing subject to a falling wave condition, which causes a boat to yaw at lower speeds of around 18 to 20 miles per hour.

It will thus be sen that I have provided means for progressively reducing the drag of the bottom of the hull of a boat as the speed thereof increases, thereby decreasing the drag and permitting higher speeds at a given power application. I have also'provided means for stabilizing a boat at higher speeds to prevent yawing and porpoising.

Having described my invention, I claim:

1. In a boat having a bottom hull defined by longitudinally extending chine lines at each edge thereof; a pair of inwardly converging diagonally extending steps in the bottom hull one of each said steps beginning at one of the chine lines extending angularly inwardly along the bottom toward the rear of the boat; anda transversely extending step formed in the hull bottom spaced from the rear of the boat, terminating and joining the diagonally disposed steps, providing a recessed area at each side of the bottom hull adjacent the diagonal steps, and a recessed area rearwardly of the transverse step.

2. The combination called for in claim 1 wherein the diagonally extending steps begin at a'point rearwardly of the center of the longitudinal length of the hull.

3. The combination called for in claim 1 wherein the recessed area rearwardly of the transverse step has outwardly diverging diagonally disposed side walls beginning at the rear ends of the diagonally disposed steps and terminating at the rear end of the recessed area rearwardly of the transverse step, and an upwardly sloping bottom Wall.

References Cited in the file of this patent UNITED STATES PATENTS 2,044,771 Carr June 23, 1936 

1. IN A BOAT HAVING A BOTTOM HULL DEFINED BY LONGITUDINALLY EXTENDING CHINE LINES AT EACH EDGE THEREOF; A PAIR OF INWARDLY CONVERGING DIAGONALLY EXTENDING STEPS IN THE BOTTOM HULL ONE OF EACH SAID STEPS BEGINNING AT ONE OF THE CHINE LINES EXTENDING ANGULARLY INWARDLY ALONG THE BOTTOM TOWARD THE REAR OF THE BOAT; AND A TRANSVERSELY EXTENDING STEP FORMED IN THE HULL BOTTOM SPACED FROM THE REAR OF THE BOAT, TERMINATING AND JOINING THE DIAGONALLY DISPOSED STEPS, PROVIDING A RECESSED AREA AT EACH SIDE OF THE BOTTOM HULL ADJACENT THE DIAGONAL STEPS, AND A RECESSED AREA REARWARDLY OF THE TRANSVERSE STEP. 